On Feb 14, 2002, to the best of my knowledge (and Google searching at the time) I coined the following from the All Your Base meme:
Rose are red
Violet are blue
All my base
Are belong to you
A variation I could find I had posted on the occasion of Rob Malda proposing in a most geekish fashion, using his own
Now it seems to be everywhere, even on shirts at thinkgeek.com (I didn't think to submit it to them so haven't seen a penny of that.)
About 4 years ago I adopted my current sig.
A feeling of having made the same mistake before: Deja Foobar
It was common to refer to a programming error as a foobar in one place I worked, as they were usually the result of testing, rather than the older acronym fubar which I felt carried a stronger definition of erring.
The sig actually was born when I was reminiscing about Deja News, perhaps due to Google's revival of the Deja archives for Google Groups and coined the term deja foobar without particularly attaching it to anything. Eventually I would associate the term with the feeling of making the feeling of repeating programming mistake. And wanting a new, more original sig for my slashdot account made it such.
This is more easy to track than the AYB poem. I was almost immediately set upon by people pointing out I had it wrong and it should be fubar. As the original meaning was rather private I didn't care and shrugged off these "correction attempts" over the years. I recently wondered if anyone had picked up the sig and posted it anywhere.
Indeed it has been, spelled foobar and fubar. Some others have even gone so far as to use it in their sig as well. The number of matches is surprising and shows how far an original idea spreads. Both are found with the core idea of 'feeling of having made the same mistake before' Interesting. I should probably post it to thinkgeek.com before someone else nicks it.